The width of the same rectangle is measured as 19.4mm correct to 1 decimal place. b) what is the lower bound for the area of the rectangle?

The definition of a rectangle is that two parallel sides are longer that the two other sides which are perpendicular at right angles. Thus, if the accuracy of measurement if only to one decimal place the longer side would have to be at least 19.5 mm. This makes the area 378.3 square mm.